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Simple HTTP client with HTTP/1.1, HTTP/2, and HTTP/3 support

Security advisory: This version has known vulnerabilities. View advisories
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hackney src hackney_metrics.erl
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src/hackney_metrics.erl 

%%% -*- erlang -*-

%%%

%%% This file is part of hackney released under the Apache 2 license.

%%% See the NOTICE for more information.

%%%

%%% Copyright (c) 2012-2026 Benoît Chesneau <benoitc@e-engura.org>

%%%



-module(hackney_metrics).

-author("benoitc").



%% API

-export([

  init/0,

  get_backend/0

]).



%% Counter operations

-export([

  counter_inc/2,

  counter_inc/3

]).



%% Gauge operations

-export([

  gauge_set/3,

  gauge_inc/2,

  gauge_dec/2

]).



%% Histogram operations

-export([

  histogram_observe/3

]).



%% Metric declarations

-export([

  declare_counter/3,

  declare_gauge/3,

  declare_histogram/3,

  declare_histogram/4,

  declare_pool_metrics/1

]).



-include("hackney.hrl").



%% Default duration histogram buckets (in seconds)

-define(DEFAULT_DURATION_BUCKETS, [0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1.0, 2.5, 5.0, 10.0]).



%% @doc Initialize the metrics system.

%% Determines the backend to use and declares all hackney metrics.

init() ->

  Backend = hackney_util:mod_metrics(),

  ets:insert(?CONFIG, {metrics_backend, Backend}),

  declare_metrics(Backend).



%% @doc Get the current metrics backend module.

get_backend() ->

  try

    ets:lookup_element(?CONFIG, metrics_backend, 2)

  catch

    error:badarg ->

      %% ETS table not ready yet, return dummy backend

      hackney_metrics_dummy

  end.



%% @doc Increment a counter by 1.

counter_inc(Name, Labels) ->

  (get_backend()):counter_inc(Name, Labels).



%% @doc Increment a counter by a value.

counter_inc(Name, Labels, Value) ->

  (get_backend()):counter_inc(Name, Labels, Value).



%% @doc Set a gauge to a value.

gauge_set(Name, Labels, Value) ->

  (get_backend()):gauge_set(Name, Labels, Value).



%% @doc Increment a gauge by 1.

gauge_inc(Name, Labels) ->

  (get_backend()):gauge_inc(Name, Labels).



%% @doc Decrement a gauge by 1.

gauge_dec(Name, Labels) ->

  (get_backend()):gauge_dec(Name, Labels).



%% @doc Observe a value for a histogram.

histogram_observe(Name, Labels, Value) ->

  (get_backend()):histogram_observe(Name, Labels, Value).



%% @doc Declare a counter metric.

declare_counter(Name, Help, LabelKeys) ->

  (get_backend()):declare_counter(Name, Help, LabelKeys).



%% @doc Declare a gauge metric.

declare_gauge(Name, Help, LabelKeys) ->

  (get_backend()):declare_gauge(Name, Help, LabelKeys).



%% @doc Declare a histogram metric with default buckets.

declare_histogram(Name, Help, LabelKeys) ->

  (get_backend()):declare_histogram(Name, Help, LabelKeys).



%% @doc Declare a histogram metric with custom buckets.

declare_histogram(Name, Help, LabelKeys, Buckets) ->

  (get_backend()):declare_histogram(Name, Help, LabelKeys, Buckets).



%% @doc Declare pool-specific metrics.

%% Called when a new pool is created.

declare_pool_metrics(_PoolName) ->

  Backend = get_backend(),

  %% Only declare once (idempotent for prometheus)

  Backend:declare_gauge(hackney_pool_free_count,

    <<"Number of free/available connections in the pool">>, [pool]),

  Backend:declare_gauge(hackney_pool_in_use_count,

    <<"Number of connections currently in use">>, [pool]),

  Backend:declare_counter(hackney_pool_checkouts_total,

    <<"Total number of connection checkouts">>, [pool]),

  ok.



%% @private

%% Declare all hackney metrics at startup.

declare_metrics(Backend) ->

  %% Request metrics

  Backend:declare_counter(hackney_requests_total,

    <<"Total number of HTTP requests started">>, [host]),

  Backend:declare_gauge(hackney_requests_active,

    <<"Number of currently active HTTP requests">>, [host]),

  Backend:declare_counter(hackney_requests_finished_total,

    <<"Total number of HTTP requests finished">>, [host]),

  Backend:declare_histogram(hackney_request_duration_seconds,

    <<"HTTP request duration in seconds">>, [host], ?DEFAULT_DURATION_BUCKETS),

  %% Pool metrics are declared when pools are created

  ok.